An adjustable resilient foot prosthesis

ABSTRACT

An artificial foot which includes a foot blade and a hollow cylindrical body which extends at an angle to the foot blade and which is connected thereto in a manner to permit relative movement therebetween. The foot also includes a two-part brace which is displaceable and adjustably mounted in an upper end of the cylindrical body and is attached to the foot blade at a lower end of the body in a manner such as to permit relative movement between the foot blade and the brace. Displaceability and adjustability of the brace, and therewith angular adjustment of the foot, may be provided by the combination of a ball screw and a ball nut which is rotatable, and selectively lockable by the user.

The present invention relates to an orthopedic foot according to thepreamble of claim 1.

It is well known that it is troublesome for people wearing a prostheticfoot to walk downhill. In those cases where the person wearing a footprosthesis is not able to adjust the foot angle, it is only the heelwhich has contact with the road surface or like surface when walkingdown a steep slope. Over a given number of degrees of foot angle, it isdifficult to hold back, or brace the body, so that the knee will notcollapse (due to the absence of important muscle groups). Consequently,the wearer of the prosthesis will often choose to walk sideways down aslope.

Furthermore, the wearer of a prosthetic foot which lacks the possibilityof adjustment in the height direction finds it problematic to change toa shoe of different heel height, and of quickly choosing to walk withoutshoes. Individual adjustment of the foot in a vertical or heightdirection also alleviates problems associated with back pains and wornhips.

An adjustable prosthetic foot is known, for instance, from the U.S. Pat.No. 2,749,557, although this prosthetic foot can only be adjusted inthree different angular positions.

The Swedish Published Specification No. 456 134 teaches a prosthesticfoot with which the angular positions thereof can be adjusted by meansof a screw provided in the heel of the foot. In order to change theangular position of the foot, it is necessary for the wearer of theprosthesis to turn the screw an appropriate number of turns, whichrequires a certain amount of effort on the part of the wearer. Theangle-changing principle taught by this publication has the seriousdrawback that the length of the leg remains changed, which means that insome positions, the wearer may limp on the right or the left leg.

One object of the present invention is to solve the aforesaid problemsand to provide an adjustable resilient foot prosthesis which can beadjusted to an innumerable number of angular positions quickly andsmoothly. Another object of the invention is to provide a footprosthesis which is light in weight and which will thrust the footforwards when a walking step is completed and which will also eliminatethose drawbacks associated with earlier known techniques. The solutionto these problems is set forth in the characterizing clause of claim 1.

FIG. 1 illustrates a preferred embodiment of the invention.

FIG. 2 is a sectional view through a hollow cylindrical body takenthrough the points at which the brace is attached to the cylindricalbody. The threads of the screw and its associated balls are drawn inanother section plane, in order to improve illustration.

FIG. 3 is a rear view of the foot.

The orthopedic foot illustrated in FIGS. 1-3 comprises a bar or footblade 1, preferably made of carbon fibre material and intended to beattached to a bottom part (not shown in the drawings) which functions asa walking sole and which is manufactured from some kind of rubbermaterial, for example. The foot blade preferably comprises two parts,namely a main blade 2 and a toe blade 3. The length of the toe blade ispreferably smaller than half the length of the main blade. The forwardpart of the main blade 2 and the rearward part of the toe blade 3 arecurved upwards such as to form therebetween a cup-shaped part 4. Aspring device 5, preferably made of an elastic material, such as rubber,is fitted in said cup-shaped part.

Arranged approximately centrally on the main blade 2 in the direction ofits longitudinal axis is an upper foot-part which includes a hollowcylindrical body 6 which is attached to the foot-blade through theintermediary of rubber spacing blocks 7, 13 so as to obtain relativemovement between the foot-blade and the upper foot-part. The upperfoot-part is intended for attachment to a lower leg-part or to someother prosthesis, in accordance with a conventional method. Thecylindrical body 6 is provided with two mutually opposed slots whichextend in the direction of the longitudinal axis of said body. A ballnut 9 is mounted on journal bearings 10 in the lower part of the tubularbody 6 so that said body can be rotated with the rotational axis lyingalong the cylinder axis of the cylindrical body. Extending in the ballnut 9 is a partially screw-threaded shaft which approximately midway ofan upper non-threaded part is connected to a two-part brace 12 whichextends from said shaft to the rear end of the foot blade 1, where it isconnected to the foot blade through the intermediary of an elasticspacing block 13. This brace is comparable to the heel tendon of thehuman foot. A moveably mounted nylon piston 14 embraces the shaft in theregion of the upper attachment point of said brace to said shaft. Onefunction of the piston is to form a support for an upper spring 15 and alower spring 16, preferably made of an elastic, rubber material, andalso to centre movement in the cylindrical body 6. The upper spring isalso supported by a washer 17 which is located on tile upper end of theshaft and which is locked by means of a nut 18. The bottom spring isalso supported by a washer 19 which is mounted at the start of thescrew-thread on the shaft, which is approximately midway along theshaft. The upper, non-threaded part of the shaft is bevelled in thelongitudinal direction, therewith to prevent rotational movement. Thethreaded part of the shaft may move freely in the ball nut, aspreviously mentioned. This movement is activated by the prosthesiswearer but can be locked, however, by preventing rotation of the ballnut 9. This is effected by applying a braking force on the outercylindrical surface 20 of the ball nut with the aid of a brake means.This brake means comprises a brake shoe or brake block 21 which liesagainst the cylindrical surface 20 when the brake is applied.

The brake means may alternatively have the form of a toothed ring placedaround the cylindrical surface 20 and a pawl which engages said toothedring when the brake is applied. This preferred variant includes a brakeshoe 21 which, via an arm 22 which extends around half the circumferenceof the cylindrical body, is attached to a brake wire 23 which extends toa height along the leg appropriate to the wearer of the prosthesis. Thecasing 24 of the brake wire is attached to the outer surface of thecylindrical body 6 by means of an attachment device. The actual wire 23itself is attached to the arm 22 via a spring 25.

The prosthestic foot functions in the following manner: When the foot isattached to the lower leg of the user and the ball nut is in its brakingposition, such that the brake shoe 21 lies against the outer cylindricalsurface 20 of the ball nut, the brace 12, which extends from thecylindrical body 6 to the foot blade 1, will function similar to theheel tendon of a human foot. The nylon piston to which the upper part ofthe brace 12 is attached moves up and down, in response to movement ofthe centre of gravity between heel and toe part. The two springs whichtransmit the force from the brace to the shaft in the ball screw thenmutually coact with the rubber springs mounted in the foot blade so thatthe foot is thrust forwards to some extent upon completion of a walkingstep.

When the wearer intends to walk down a steep slope or to change theangle of the foot for some other reason, for instance to change shoes,etc., the wearer manoeuvres the brake wire so that the brake shoe willno longer abut the ball nut. The shaft extending through the ball nutcan now be moved axially, thereby rotating the ball nut. Adjustment tothe desired angular position can be effected by applying a requisiteforce on the toe part or the heel part of the prosthestic foot.

The use of a ball nut and associated spindle has made it possible withinprosthesis technique to convert linear motion to rotational motion witha limited force. The realization of this with this particularapplication is fundamental to the advent of this prosthesis.

The inventive prosthetic foot has many advantages. It stands flat andstable on the underlying support surface.

It constantly follows the direction in which the user walks, whicheliminates wear on hip joints and on the spine.

The angle of the foot can be adjusted so as to enable the wearer to useshoes of differing heel heights and enables the angle of the foot to bereadily adjusted to conform to the nature of the underlying supportsurface.

It will be understood that the present invention is not restricted tothe aforedescribed and illustrated embodiment and that modifications andchanges can be made within the scope of the invention as defined in thefollowing claims.

I claim:
 1. An artificial foot comprised of:a foot blade and a hollowhousing, wherein said foot blade extends at an angle to and is connectedto said housing so as to permit relative movement between said housingand said foot blade, an elongated brace for adjusting the angularposition of said foot blade with respect to said housing, wherein oneend of said brace is displaceably and adjustably attached to saidhousing by means of attachment to a shaft with a ball screw engaged witha ball nut disposed within said housing, wherein the other end of saidbrace is connected to said foot blade so as to permit relative movementbetween said housing and said foot blade, and brake means forselectively locking and unlocking said ball nut with respect to saidhousing in order to adjust the angular position of said foot blade withrespect to said housing.
 2. An artificial foot according to claim 1,further comprising a nylon piston attached to said brace and engagingsaid shaft by means of springs when said ball nut is locked or unlockedwith respect to said housing.
 3. An artificial foot according to claim2, further comprising a brake shoe to selectively either abut said ballnut to prevent rotational movement of said ball nut, or allow rotationalmovement of said ball nut.
 4. An artificial foot according to claim 3,further comprising an arm mounted to said brake shoe and a brake wireattached to said arm, whereby said brake wire may be manipulated in aregion near the thigh of a wearer of said artificial foot in order toselectively lock and unlock said ball nut.